A special primary in Massachusetts next week will likely add diversity to the state’s congressional delegation — part of a larger shift in Bay State politics over the past few years.

On Oct. 15, a handful of top Democratic candidates will run in the definitive special primary for the open 5th District. The suburban Boston district is a strong Democratic seat and the nominee will likely take the House seat that Sen. Edward J. Markey held for decades.

Two of the top candidates are women, one is of Armenian descent, and another is openly gay. The winner could continue an evolution for the Bay State — historically one of the least diverse congressional delegations, especially for a traditionally liberal state. Since 1789, the state has only elected five women to Congress — two in the past five years — and has only had two black members, according to the House historian.

Local Democratic operatives characterized two female candidates — state Sens. Katherine Clark and Karen Spilka — as part of a trio of front-runners. But any one of the five candidates could win the low-turnout contest.

“Whoever can hold on to their base, cherry-pick their way to some additional voters and not lose people to other candidates will win,” Democratic consultant Mary Anne Marsh said.

Clark has led in public polls for the entirety of the race. Backed by EMILY’s List, she also boasts a cash advantage: She raised more than $365,000, plus put $250,000 of her own funds into the contest.

Spilka, too, has been a front-runner since she entered the contest, according to local operatives and public polling on the race.

If elected, Clark or Spilka would become the third woman elected to the Massachusetts congressional delegation since 2007. That year, Democratic Rep. Niki Tsongas came to Capitol Hill via a special election, ending the Bay State’s 25-year dearth of female members. Last year, Democrat Elizabeth Warren became the first female senator elected in the state’s history.

Democratic operatives say Middlesex County Sheriff Peter Koutoujian is also one of the top three candidates with a shot of winning Tuesday’s primary. If successful, Koutoujian would be one of just a few Armenian-Americans in Congress, joining Rep. Anna G. Eshoo, D-Calif.

Koutoujian tapped into the district’s large Armenian population in Watertown, Mass., to raise more than $600,000 for the race.

State Rep. Carl Sciortino, who is openly gay, also has a shot at winning the seat and joining the six openly gay or bisexual members of Congress.

Sciortino has been gaining in polls since he released an attention-grabbing ad last month. In the spot, Sciortino “came out” as a “Massachusetts liberal” to his father, a tea party member.

But local operatives caution that while Sciortino’s ad raised his profile, he is still not among the top-tier candidates in the contest. Instead, local hired hands say, he could serve as a spoiler for Clark, Spilka or Koutoujian.

While the ad “certainly lifted him in the polls, it was not to a degree that puts him in front-runner status,” a top Massachusetts Democratic consultant said. “Instead he’s taking away votes from other people.” Another candidate, state Sen. William Brownsberger, who has polled at the bottom of the pack in the contest, was also mentioned as a potential spoiler.

Every vote will count in this contest, which is expected to have record-low turnout. Local operatives attribute this to a fatigued voter base, thanks to a near constant state of campaigning in Massachusetts.